In said system the transformer is the electrical link between the high voltage transmission system and the local distribution system. The output from the transformer is connected to a separate distribution or switchboard unit connecting the transformer to the user equipment.
Transformers for subsea installations customary consist of a chamber housing the transformer proper with core and copper windings. This chamber is filled with transformer oil. To balance the internal pressure of the chamber to the ambient seawater pressure, the transformer assembly is equipped with a volume compensator in the form of an external expansion chamber.
This compensator constitutes a barrier against the surrounding water that is important for the correct operation of the transformer. Water leaking into the transformer chamber can cause electric shorts between the windings, which damages the transformer. The oil has very little ability to absorb contaminant water. To maintain this barrier intact is a problem for the manufacturer as the unit experiences a great span of pressures from the surface down to the sea bottom. An eventual leak will also pose a pollution problem.
The distribution unit is contained in its own oil filled housing with pressure compensation mechanism, separate from the transformer housing.